1. Technical Field
The present invention relates to a green emitting yttrium silicate phosphor and a cathode-ray tube using it, more particularly to a green emitting yttrium silicate phosphor, which has an improved temperature characteristic and life, and a cathode-ray tube using it.
2. Description of Related Art
In these years, cathode-ray tubes, such as a color cathode-ray tube (CRT), a projection cathode-ray tube (PRT), a field emission display (FED), and a vacuum fluorescent display (VFD), are getting to display a higher resolution image in higher brightness for responding needs. Phosphors used in these cathode-ray tubes are required to be further improved. Particularly, since a projection cathode-ray tube projects and displays an enlarged image, a higher brightness is required compared with a direct-view tube, and a high voltage and a high current are applied thereto. Accordingly, phosphors, which have good characteristics, such as a high resistance against high load, a brightness saturation characteristic, a temperature characteristic and its life, are necessary. Among phosphors, since a green emitting phosphor highly contributes to white, requirements on it is also high, and various phosphors have been studied.
Hereafter, a projection cathode-ray tube is described as an example of a typical cathode-ray tube. A projection type television displays an enlarged image composed of red, green and blue light emitted from three small monochromatic cathode-ray tubes (projection cathode-ray tubes). Since the projection cathode-ray tube is used as the light source, a fluorescence surface is subjected to double digits the load as compared with a direct-view-type cathode-ray tube. For this reason, the following requirements exist on such a projection cathode-ray tube.    (1) High luminance efficiency,    (2) Proportional relationship between its luminance and a current density (brightness saturation characteristic),    (3) No luminance reduction as temperature rise (temperature characteristic),    (4) No time-variation of its luminance (life), and so on.
An yttrium silicate phosphor with the above characteristics is in actual use as a green emitting phosphor for projection cathode-ray tubes. However, as recently digital broadcasting becomes widespread, it is required to display a higher resolution image in higher brightness, and such a phosphor is subjected, to a higher load. Accordingly, further improvement of characteristics is necessary. Particularly, an yttrium silicate phosphor has a problem, of its temperature characteristic and life. High requirements for improvement of these characteristics exist.
Although Patent Document 1 and or the like discloses improvement of the temperature characteristic and life of the yttrium silicate phosphor for the projection cathode-ray tubes, since a phosphor is subjected to a higher load in recent years, further improvement is still necessary. Although Patent Documents 2 and 3 disclose that substituting Sc for a part of phosphor composition improves luminance, the disclosed compositions do not sufficiently improve their temperature and life characteristics. Accordingly, improvement is still necessary.    Patent Document 1: Japanese Laid-Open Patent Publication TOKUKAI No. HEI 9-316444.    Patent Document 2: Japanese Laid-Open Patent Publication TOKUKAI No. SHO 56-167783.    Patent Document 3: Japanese Laid-Open Patent Publication TOKUKAI No. SHO 62-260885.